The aim of the project is to ensure sustainable milk production from healthy goats by achieving new knowledge on the causes of high numbers of somatic cells counts (SCC) in Norwegian goat milk, and its further importance for cheese yield and quality. This knowledge also has relevance for cow's milk. The project started in May 2021 and ends in 2024 and is funded by the Research Levy for Agriculture and Food Industry (FFL/JA). Project leader is Professor Siv Skeie at NMBU, and partners are TINE, NSG and Agroscope (Switzerland).
Rangeland pasture is an important feed source for dairy goats and has many positive side effects. However, at rangeland pasture and at oestrus, an increase in SCC is often observed in milk, even without signs of clinical mastitis in the goats. Knowledge about the types of somatic cells present in milk and how these cells affect product quality is lacking. Reduced payments for milk due to high SCC may lead to reduced use of rangeland pasture. The project is therefore important to gain knowledge and understanding on how SCC affects raw milk quality, technological properties of milk and product quality.
The milk somatic cells consist of milk producing cells (epithelial cells) and immune cells (leukocytes). Immune cells can release enzymes at varying degrees, which can impair product quality. In this project, we will use a flow cytometer to develop methods to sort and differentiate the cells and divide the immune cells into neutrophilic cells, macrophages and different types of lymphocytes. This enables us to study the kind of cells present in the milk at different grazing conditions, at udder infections and at oestrus. Furthermore, enzymes and inflammation markers in/from the different types of cells can be characterised. These analyses can then be linked to SCC, microbiology, milk composition and cheese technology characteristics of the milk.
Few studies have been done on SCC in goat milk and their impact on cheese quality. Data from previous studies on Norwegian goats indicate that cheese making properties are negatively affected by cell counts > 1.6 million. Therefore, it is a dilemma that we aims to increase rangeland grazing, while at the same time we observe a strong increase of SCC during the grazing period.
The project is divided into 5 work packages (WP). WP1 focuses on the biological causes of variation of SCC and aims to answer which cell types are present in goat milk and how they vary under different conditions such as pasture, oestrus and udder infections, as well as the relationship between SCC and stress markers in milk. WP2 studies the effect of SCC on the composition of milk and microbiota, with a particular focus on milk proteins. WP3 focuses on the influence of SCC on cheese making properties, cheese maturation and product quality. WP4 will gather experience from Switzerland, which also uses rangeland and mountain dairy farms (Alps) to a large extent during summer. WP 5 is responsible for the active transfer of knowledge to the goat farmers and the collection of data from producers in the form of milk samples, analysis of control and udder milk samples, questionnaires, etc.
Results: Data from the national goat control (>1 mill. goat control samples and > 20 000 teat samples) were examined and showed that normal SCC in goatmilk varies strongly with parity and lactation stage. The effect of the lactation stage is difficult to distinguish from the effect of season/grazing period, as we have mainly spring kidding in Norway. SCC increases more during the season in older goats, than in younger goats, and older goats have a more distinct SCC peak around oestrus/mating. The udder samples showed that Staphylococci (S.) predominated in infected udder samples. S. aureus infections were more common in younger goats than in older. The highest SCC was found in goats infected with S. aureus, but also S. warneri and streptococci lead to an increase in SCC. The study concluded that SCC is a quite good indicator of infection if the threshold values are adapted to parity and lactation stage. The results of the study are published in the Journal of Dairy Science.
Ongoing activities: Cheese making experiments focusing on the influence of SCC on cheese making properties of the milk and cheese quality are in progress. We collected milk from 4 herds at 4 different times: Before letting out on pasture (May), right after letting out on rangeland pasture (June), during rangeland grazing (July) and at oestrus (Sept.). We have also taken teat samples and goat control samples from all goats in the herds included in the study, and a questionnaire has been sent out to all goat milk producers. A Manchego-type cheese and a Feta-type cheese has been made from milk of each herd. For both cheese types we are investigating whether there is an effect of SCC on cheese yield and cheese quality. The cheeses are now ripening, and we are eagerly waiting for answers.
The Norwegian dairy industry observe that the somatic cell count (SCC) often increases when dairy goats are let out on rangeland pasture and during oestrus. However, in goats, a high SCC is also observed in milk without signs of clinical mastitis, There is limited knowledge on how the content and type of SCC in goat milk varies between individual goats and over the course of lactation, and also on how they are influenced by pasture. Moreover, the effects of the SCC on product quality remain largely unknown. Therefore, knowledge of how, and to what extent SCC affects milk- and product quality especially during the pasture period, is of great importance for the future of the Norwegian goat milk production. The novelty of the project is the combination/integration of high-resolution characterization of the somatic cell types by flow cytometry and goat milk composition (chemical and microbial) and goat milk processing aimed towards the production of increased value dairy products from goat milk. Goat milk SCC aims at securing a sustainable goat milk production from healthy goats by providing novel insights on reasons for high number of somatic cell counts (SCC) in Norwegian goat milk and its influence on the yield and quality of goat milk products.